Hallo Fiona,
guck mal ob dir das was hilft:
<html>
<head>
<title>Probe</title>
<meta name="author" content="Bernhard Wagner">
<script type="text/javascript">
<!--
var vor;
var numm;
function hopp(hinn,num, ho){
if(ho==0){
document.getElementById("hin").disabled = false;
document.getElementById("her").disabled = true;
}
if(ho==1){
document.getElementById("her").disabled = false;
document.getElementById("hin").disabled = true;
}
vor = hinn;
numm = num;
}
function hilf(li,re) {
neues = new Option(vor);
document.getElementById(li).options[document.getElementById(li).length] = neues;
document.getElementById(re).options[numm] = null;
document.getElementById("hin").disabled = true;
document.getElementById("her").disabled = true;
}
//-->
</script>
<noscript></noscript>
</head>
<body >
<form action="" method="" target="">
<table width="770" align="center">
<tr>
<td><select id="stra" size="10" style="width:300;" onChange="hopp(this.form.stra.options[selectedIndex].text, this.form.stra.options.selectedIndex, 0)">
<option value="">Abbau</option>
<option value="">Am Bahnhof</option>
<option value="">Andreasberg</option>
<option value="">Anger</option>
<option value="">Bahnhof</option>
<option value="">Bahnhofstraße</option>
<option value="">Bergstraße</option>
<option value="">Elbingerstraße</option>
</select></td>
<td align="center">
<input type="Button" id="hin" value="hin >>>" style="width:100;" onClick="hilf('stru','stra')" disabled><br><br>
<input type="Button" id="her" value="<<< her" style="width:100;" onClick="hilf('stra','stru')" disabled></td>
<td> <select id="stru" size="10" style="width:300;" onChange="hopp(this.form.stru.options[selectedIndex].text, this.form.stru.options.selectedIndex, 1)"></select></td>
</tr>
</table>
</form>
</body>
</html>
Gruß Bernhard